Conventional nanosecond pulsed-laser melt annealing (“conventional melt laser annealing”) offers an ultra-low thermal budget, high dopant activation and super-abrupt junctions that are ideal for advanced integrated circuit (IC) chip fabrication. In practice, however, it is difficult to implement this type of annealing on patterned wafers due to large temperature non-uniformities that can arise from spatial variations in the optical and thermal properties of the IC chip. These adverse effects are referred to in the art as “pattern density effects.”
U.S. Pat. No. 8,309,474 describes a technique where a first scanned laser beam is used to pre-heat a substrate to near-melt conditions in a uniform manner using a hybrid melt/non-melt apparatus. A second laser that emits a light beam with light pulses is then used to bring the annealed region up to the melt temperate for a short period that allows the melted region to recrystalize quickly. An advantage of this approach is that the temperature non-uniformity from the pulsed laser interacting with the patterned substrate is significantly mitigated. However, this approach suffers from pulse-to-pulse repeatability requirements and pulsed laser image uniformity constraints, and also has a relatively long dwell time in the range of 100 microseconds to 20 milliseconds that exacerbates the above-mentioned issues.
U.S. Pat. No. 8,865,603 describes an annealing system wherein a scanning continuous wave (CW) laser beam is used to perform backside laser processing with dwell times in the range from 1 microseconds to 100 microseconds. The advantage of this approach is that the beam stability can be much better than 1% and the beam uniformity at the wafer is defined by the Gaussian profile, which is well understood. Unfortunately, the power requirements and the dwell time requirements of this approach are far too long to allow for fast recrystalization of the melted substrate.